1. Field of the Invention
The present invention relates to a shift register, a liquid crystal display (LCD) device having the shift register and a method of driving scan lines using the same.
2. Description of the Related Art
An LCD device has advantages over other display devices, for example CRT type display device. In detail, the LCD device may be manufactured in a thinner and lighter structure having a lower power consumption, may require a lower driving voltage compared with the other display devices, and may provide image display quality similar to that of the CRT type display device. The LCD device is widely used in various electronic apparatus.
When voltage is applied to liquid crystal molecules, the alignment angle of the liquid crystal molecules is changed, the transmissivity of the liquid crystal molecules is regulated, and thus an image is displayed.
The LCD device is classified into a twisted nematic (TN) type LCD device and a super-twisted nematic (STN) type LCD device. The LCD device also may be classified into an active matrix type LCD device and a passive matrix type LCD device according to a method of driving the LCD device. The active matrix type LCD device employs switching elements and TN liquid crystal. The active matrix type LCD device is used in a thin film transistor (TFT) LCD device. However, the passive matrix type LCD device employs STN liquid crystal.
The active matrix type LCD device uses the thin film transistors as a switching element so as to drive the LCD device. However, the passive matrix type LCD device does not use transistors so as to drive the LCD device, so that the passive matrix type LCD device does not require complicated circuits for driving the LCD device.
The TFT LCD device is classified into amorphous-Si TFT LCD (or a-Si TFT LCD) device and a poly-Si TFT LCD device. The poly-silicon TFT LCD (or poly-Si TFT LCD) device has lower power consumption and a low price, but is manufactured through complex processes compared with the a-Si TFT LCD device. Accordingly, the poly-Si TFT LCD is used in a display device having a small display screen such as a mobile phone.
The a-Si TFT LCD device may provide a large display screen and a high yield (or high productivity), and is used in a display device having a large display screen such as a laptop computer, an LCD monitor or a high definition television (HDTV).
FIG. 1 is a schematic view showing a conventional poly-silicon thin film transistor LCD, and FIG. 2 is a schematic view showing a conventional a-Si thin film transistor LCD.
As shown in FIG. 1, the poly-Si TFT LCD device includes a poly-Si TFT pixel array formed on a glass substrate 10. A data driver circuit 12 and a gate driver circuit 14 are formed on the glass substrate 10. An integrated printed circuit board 20 is connected to a terminal part 16 by means of a film cable 18, so that the cost for manufacturing the poly-Si TFT LCD device may be reduced and power consumption may be minimized because the data driver circuit 12 and the gate driver circuit 14 are integrated on the glass substrate 10.
However, as shown in FIG. 2, in the a-Si TFT LCD device, a data driver chip 34 is mounted on a flexible printed circuit board 32 via a chip on film (COF), and a data printed circuit board 36 is connected to a data line terminal on the a-Si TFT pixel array through the flexible printed circuit board 32. A gate driver chip 40 is mounted on the flexible printed circuit board 32 via the chip on film (COF), and a gate printed circuit board 42 is connected to a gate line terminal on the a-Si TFT pixel array through a flexible printed circuit board 40.
The a-Si TFT LCD device has an advantage in aspect of yield (or productivity), but has disadvantage in aspect of manufacturing cost and thickness.
A power supply for supplying a power voltage to the gate driver circuit may be mounted on the data printed circuit board so as to remove the gate printed circuit board.
However, even when the gate driver circuit is mounted on the data printed circuit board, the gate driver circuit is mounted on the flexible printed circuit. Since a plurality of flexible printed circuits is bonded to the glass substrate, the a-Si TFT LCD device uses a complicate outer lead bonding process so as to bind the flexible printed circuits to the glass substrate. Accordingly, the cost for manufacturing the a-Si TFT LCD device increases.
Therefore, according to a recent method of manufacturing the a-Si TFT LCD device, the data driver circuit and the gate driver circuit are formed on the glass substrate in the same process as the process of forming the pixel array on the glass substrate so as to reduce the number of steps for manufacturing the a-Si TFT LCD device.
However, the shift direction is fixed in the shift register of the conventional a-Si TFT LCD device, and the conventional a-Si TFT LCD device does not provide a bi-directional shift register in which a forward shift or a backward shift occurs.